Non-specific environmental stress in early embryogenesis, e.g. heat shock, anoxia or chemical exposure, can lead to remarkably specific developmental defects. For example, in humans and other mammals, exposure to extreme heat can lead to neural tube defects, and exposure to alcohol can lead to a characteristic spectrum of defects, in the most severe cases characterized as fetal alcohol syndrome. The project focuses on similar effects in the model system of Drosophila melanogaster in which the developmental defects have been termed phenocopies for their ability to mimic the phenotypes of specific genetic mutations. Many of these phenocopy defects arise due to the effects of environmental stress on the patterning of cell fate specifications across the embryo; however, others arise from stresses that occur after cells have committed to specific cell fates. In the latter case, the defect is caused by errors in the process by which committed cells drive morphogenesis through spatiotemporal regulation of cell- and tissue-level biomechanics. This project will focus on one example of this effect - heat shocks during the gastrulation stage of embryogenesis that lead to developmental defects some 4-5 hours later during the germband-retraction stage. The project seeks to explain how aberrant cell behaviors and cell division patterns induced by the heat shock later lead to altered tissue biomechanics and hence a developmental defect. Methods to be used include time-lapse confocal imaging of GFP-labeled Drosophila embryos, laser-microsurgery to probe the biomechanics in vivo, laser-induced heat shocks of local regions within the embryos, and an advanced computational method called video force microscopy (VFM) that uses an inverse finite element method to infer cellular forces from time-lapse images of moving/deforming tissues. The four specific aims of this project are: 1. To evaluate the correlation between an extra 14th mitosis in the amnioserosa - a tissue which plays a critical mechanical role in embryogenesis - and subsequent defects in germband retraction 2. To confirm the specificity of this correlation using local, laser-induced heat shocks delivered only to cells of the presumptive amnioserosa 3. To evaluate the cell- and tissue-level forces that are altered by heat-shock and the means by which these altered forces lead to defects in germband retraction using video force microscopy (VFM) 4. To validate the dynamic force maps obtained by VFM and challenge our mechanical hypothesis with laser-microsurgery Once complete, the results from these four aims should paint the most complete picture available for the biomechanical chain of events that leads from an environmental stress in early embryogenesis to a later developmental defect.